Plant Ecology

, Volume 216, Issue 10, pp 1441–1456 | Cite as

Patterns of CO2 exchange and productivity of the herbaceous vegetation and trees in a humid savanna in western Kenya

  • Dennis Otieno
  • Joseph Ondier
  • Sebastian Arnhold
  • Daniel Okach
  • Marianne Ruidisch
  • Bora Lee
  • Andreas Kolb
  • John Onyango
  • Bernd Huwe
Article

Abstract

Factors governing the dynamics between woody and herbaceous vegetation in the savanna are of ecological interest since they determine ecosystem productivity and stability. Field measurements were conducted in a humid savanna in the Lambwe valley, western Kenya, to compare CO2 exchange of the herbaceous vegetation and trees and its regulation. Soil characteristics and root distribution patterns under tree canopies and in the open locations dominated by the herbaceous vegetation were profiled in 1-m-deep soil layers. Soil water content (SWC) was measured at 30 cm depth both in the herbaceous vegetation and also under the tree canopies. The mean maximum monthly gross primary production (GPPmax) in the herbaceous vegetation was determined from chamber measurements, while daily GPP (GPPday) in both the grass and tree canopies was simulated using the PIXGRO model. The highest mean GPPmax in the herbaceous vegetation was 26.2 ± 3.7 μmol m-2 s-1 during April. Seasonal fluctuations of GPP in the herbaceous vegetation were explained by soil water availability (R2 = 0.78) within the upper 30-cm soil profile. Seasonal GPPday fluctuations were larger (between 1 gC m-2 d-1 and 10 gC m-2 d-1) in the herbaceous vegetation compared to the trees, which fluctuated around 4.3 ± 0.3 gC m-2 d-1 throughout most of the measurement period. Daily tree canopy transpiration (Ec), canopy conductance (Gc), and GPPday were decoupled from SWC in the top 30-cm soil profile. On average, ecosystem GPPday (mean of tree and herbaceous vegetation) was 14.3 ± 1.2 gC m-2 d-1 during the wet period and 6.1 ± 0.9 gC m-2 d-1 during drought. Differences between the herbaceous and tree canopy responses were attributed to soil moisture availability.

Keywords

Canopy conductance Canopy transpiration Gross primary production Hydraulic lift Humid savanna Soil water availability 

Supplementary material

11258_2015_523_MOESM1_ESM.docx (38 kb)
Supplementary material 1 (DOCX 37 kb)
11258_2015_523_MOESM2_ESM.doc (26 kb)
Supplementary material 2 (DOC 25 kb)

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Copyright information

© Springer Science+Business Media Dordrecht 2015

Authors and Affiliations

  • Dennis Otieno
    • 1
  • Joseph Ondier
    • 2
  • Sebastian Arnhold
    • 3
    • 4
  • Daniel Okach
    • 1
  • Marianne Ruidisch
    • 1
  • Bora Lee
    • 1
  • Andreas Kolb
    • 3
  • John Onyango
    • 2
  • Bernd Huwe
    • 3
  1. 1.Department of Plant EcologyUniversity of BayreuthBayreuthGermany
  2. 2.Department of BotanyMaseno UniversityMasenoKenya
  3. 3.Department of Soil PhysicsUniversity of BayreuthBayreuthGermany
  4. 4.Professorship of Ecological ServicesUniversity of BayreuthBayreuthGermany

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